1. Field
The following description relates to transmitters and receivers in frequency modulation-ultra-wideband (FM-UWB) communication systems.
2. Description of the Related Art
Ultra-wideband (UWB) has drawn attention as a very promising technology in the fields of wireless communications, imaging, and sensors, as its capabilities of transmitting multimedia data at a high speed of hundreds of megabits per second (Mbps) to 1 gigabit per second (Gbps) and of detecting a precise location are highlighted. As UWB has been permitted for commercial use in the field of wireless communications, various attempts have been made to use UWB in short-range wireless personal area networks.
The Federal Communications Commission in the United States has defined UWB as a wireless communication technology including a spectrum that occupies a bandwidth greater than or equal to 20% of a center frequency, or a bandwidth of at least 500 megahertz (MHz). Accordingly, existing carrier modulation including a spectrum that occupies a bandwidth of at least 500 MHz may be considered as UWB. In general, UWB is regarded as a low-power, high-speed, short-range wireless communication technology that may perform communication in a range from 3.1 to 10.6 gigahertz (GHz) at a rate of 100 Mbps or more over a band wider than that of a conventional communication technology. UWB uses an extremely wide band, and requires relatively low power. A UWB system is based on a lower power spectral density over a very wide frequency band than that of a conventional narrowband system or a wideband code division multiple access (CDMA) system. Since the UWB system spreads and transmits a signal over a bandwidth of several GHz in order to prevent interference with another communication system, the UWB system may provide communications without interfering with another narrowband signal and without being greatly affected by a frequency. As a result, the UWB system may share a frequency spectrum and require very low power. UWB has been studied in Institute of Electrical and Electronics Engineers (IEEE) 802.15.3a, which is a UWB standard for a wireless personal area network (WPAN), and in IEEE 802.15.4A, which is a UWB standard for a low-rate and low-power WPAN including a wireless positioning function.
Unlike a conventional wireless communication system using a continuous sine wave signal, an impulse radio (IR)-UWB system includes a transmitter that discontinuously transmits a Gaussian monocycle pulse or a pulse with a narrow width of 1 nanosecond (ns) or so. Accordingly, the IR-UWB system may transmit a signal using a much wider band (hundreds of MHz to several GHz) than a data modulation band, and thus, may greatly reduce a power spectral density, thereby reducing interference. Also, since the IR-UWB system uses such a pulse, the IR-UWB system is very resilient to multi-path fading. Unlike a conventional wireless communication system that puts a signal to be transmitted on a carrier, performs upward modulation and amplification of the signal, and transmits the modulated and amplified signal, the IR-UWB system modulates a baseband signal into an impulse signal, and directly transmits the impulse signal. Accordingly, the IR-UWB system may be simply constructed at low cost.